Unit 3 Cellular Energetics

What are Enzymes?

• Enzymes are biological catalysts that speed up biochemical reactions

• Enzymes are macromolecules

• Most enzymes are PROTEINS

• Enzyme structure is very specific resulting in each enzyme only facilitating one type of reaction

  • Tertiary shape must be maintained for functionality

  • Have a region called an active site

What does the active site interact with?

• A molecule that can interact with an enzyme (active site) is the substrate

  • Enzymes have an active site, which SPECIFICALLY interacts with the substrate

    • Has a unique shape and size

    • Can have chemical charge(s) or not

    • Physical and chemical properties of the substrate MUST be compatible

    • SLIGHT changes can occur to align with substrate

      

How do enzymes function in synthesis or digestion reactions/hydrolysis?

• Enzyme names often indicate the substrate or chemical reaction involved

  • Enzyme names often end in -ase

  • Ex. Sucrase is an enzyme that digests sucrose

• Enzymes are reusable

  • Not chemically changed by reaction

  • Cells typically maintain a SPECIFIC ENZYME concentration

How do enzymes affect the rate of biological reactions?

• All biochemical reactions require initial starting energy, called activation energy

• Some reactions result in a net RELEASE of energy, and some reactions result in a net ABSORPTION of energy

• Typically, reactions resulting in a net release of energy REQUIRE LESS ACTIVATION energy compared to reactions resulting in net absorption of energy

• Enzymes LOWER the activation energy requirement of all enzyme-mediated reactions, accelerating the rate of reactions

What is a controlled experimentand what are the two types?

• A scientific investigation

• Two types of tests set up in a controlled experiment

  • Control test (group)

    • Generates data under conditions with no treatment/no manipulation

    • Generates data under normal/unchanged conditions

    • Considered baseline data

  • Experimental test (group)

    • Generates data under abnormal/unknown conditions

    • Generates data under treated/manipulated conditions

    • Test results are often compared with control test results to help determine possible impacts of a treatment/manipulation

What is a controlled group used for?

• Used for comparison

  • Negative Control

    • Not exposed to the experimental treatment or any treatment known to have an effect

  • Positive Control

    • Exposed to a treatment that has a known effect

    • Not exposed to the experimental treatment

  • Both types of controls can be used to validate experimental procedures

*Controlled variables are aspects of an experiment that could be changed but are intentionally not changed

What changes to the molecular structure of an enzyme result in denaturation?

• Changes in the conformational shape of the enzyme

• Changes in environmental temperature

• Changes in environmental pH

• Enzyme denaturation is TYPICALLY IRREVERSIBLE, and the catalytic ability of the enzyme is lost or severely decreased

• HOWEVER, in some cases, enzyme denaturation is reversible, regaining the catalytic ability

What are the effects of enzyme activity efficiency from environmental temperature?

• Optimum temperatures

  • Range in which enzyme-mediated reactions occur the fastest

  • Reaction rates change when the optimum temperatures aren’t maintained

• Environmental increase in temperature

  • Initially increases reaction rate

    • Increased speed of molecular movement

    • Increased frequency of enzyme-substrate collisions

  • Temperature increases outside of the optimum range result in enzyme denaturation

• Environmental decrease in temperature

  • Generally slows down the reaction rate

    • Decreased frequency of enzyme-substrate collisions

    • Does not disrupt enzyme structure, no denaturation

What are the effects of enzyme activity efficiency from environmental pH?

• pH measures the concentration of hydrogen ions in solution

  • Measured on a logarithmic scale

  • Small changes in pH values equate to large shifts in hydrogen ion concentration

  • Ex. pH 6 has 1ox more hydrogen ions in solution compared to pH 7

• Optimum pH

  • Range in which enzyme-mediated reactions occur the fastest

  • Changing the pH outside of this range will slow or stop enzyme activity

  • Enzyme denaturation can occur as a result of increases and decreases outside of the optimum range

  • Changes in hydrogen ion concentration can disrupt hydrogen bond interactions that help maintain enzyme structure

How does concentrations of substrates and products affect the reaction rate

• Initial increases in substrate concentration increase reaction rate

  • More substrates mean more opportunity to collide with the enzyme

• Substrate saturation will eventually occur

  • Results in no further increase in rate

  • Reaction rate will remain constant if saturation levels are maintained

• Increased concentration of products decreases the opportunity for the addition of substrate

  • Matter takes up space

  • More products in an area means a lower chance of enzyme-substrate collisions

  • Slows reaction rate

How does enzyme concentration impact reaction rate?

• Less enzyme = slower reaction rate

  • Less opportunity for substrates to collide with active sites

• More enzyme = faster reaction rate

  • More opportunity for substrates to collide with active sites

What are competitive inhibitors?

• Molecules that can bind reversibly or irreversibly to the active site of the enzyme

  • COMPETES with the normal substrate for the enzyme’s active site

  • If inhibitor concentrations exceed substrate concentrations, reactions are slowed

  • If inhibitor concentrations are considerably lower than substrate concentrations, reactions can proceed normally

  • If inhibitor binding is irreversible, enzyme function will be prevented

  • If the inhibitor binds reversibly, the enzyme can regain function once the inhibitor detaches from the active site

What are no competitive inhibitors?

• Enzymes can have regions other than the active site to which molecules can bind, called an allosteric site

• Noncompetitive inhibitors

  • DO NOT bind to the active site

  • BINDS to the allosteric site

  • Binding causes conformational shape change

  • Binding prevents enzyme function because the active site is NO LONGER available

  • Reaction rate decreases

• Increasing the substrate cannot prevent the effects of noncompetitive inhibitor binding

Why do all living system require constant input of energy

• Sunlight is the main energy input for living systems

• Autotrophs capture energy from physical sources, like sunlight, or chemical sources, and transform that energy into energy sources, usable by all cells.

• During every energy transformation process, some energy is unusable, often lost as heat

Life requires a highly ordered system and does not violate the second law of thermodynamics

• Every energy transfer increases the disorder of the universe

• Living cells are not at equilibrium; there is a constant flow of materials in and out of the cell

• Cells manage energy resources by energy coupling. Energy-releasing processes drive energy-storing processes,

How are pathways in the biological system sequential?

• Within a chemical pathway, the product of one reaction can serve as a reactant in a subsequent reaction.

• The sequential reaction allows for a more controlled and efficient transfer of energy

What is photosynthesis?

• The biological process that captures energy from the Sun and produces sugars

• Evidence supports the claim that prokaryotic photosynthesis by organisms, such as cyanobacteria, was responsible for the production of oxygen in the atmosphere

• Photosynthetic pathways are the foundation of eukaryotic photosynthesis

Light-dependent reactions of photosynthesis in eukaryotes involve a series of pathways

• Light-dependent reactions capture light energy by using light-absorbing molecules called pigments

• Pigments help transform light energy into chemical energy

• Chemical energy is temporarily stored in the chemical bonds of carrier molecules, called NADPH.

• Light-dependent reactions help facilitate ATP synthesis

• ATP and NADPH transfer stored chemical energy to power the production of organic molecules in another pathway called the Calvin cycle

• Oxygen is produced as a result of water hydrolysis

What is the role of chlorophyll in photosynthesis?

• Capture energy from sunlight and convert it to high-energy electrons

What happens to chlorophyll electrons when light absorption occurs, and what is the importance of this?

• Electrons will be energized. The energy from the electrons will be used to establish a proton gradient and reduce NADP+ to NADPH

What is a photosystem?

• A photosystem is a light-capturing unit in a chloroplast’s thylakoid membrane.

Why is the hydrolysis of water necessary as it relates to PSII and the light-dependent reactions?

• The hydrogen molecules from the splitting of water are released into the thylakoid space and used to create an electrochemical/proton gradient

How are PSII and PSI functionally related to the electron transport chain (ETC)?

• They pass as high-energy electrons to the ETC.

What is an electrochemical/proton gradient?

It is a difference in concentration of protons (Hydrogen ions) across a membrane.

What is ATP synthase?

• ATP synthase is an enzyme that creates ATP when protons pass through the enzyme

*Photosynthesis uses a form of passive transport to generate ATP from ADP

What does the Calvin cycle use?

ATP, NADPH, CO2, and produces carbohydrates

What is the ultimate goal of the Calvin cycle reactions?

• Make organic products that plants need using the products from light reactions of photosynthesis

Where do plants and other organisms mainly get their carbon dioxide from?

• Plants and other organisms mainly get their carbon dioxide from the environment

Fermentation and cellular respiration are processes that allow organisms to use energy stored in biological macromolecules

• Cellular respiration and fermentation are characteristics of all forms of life

• Releasing chemical energy from organic molecules, like glucose

• OXYGEN IS NOT USED during the process of FERMENTATION but is USED during the process of CELLULAR RESPIRATION

• Fermentation and anaerobic respiration are not the same.

  • Products of fermentation are lactic acid or ethanol

  • Anaerobic respiration still has pyruvate

Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that capture energy from biological macromolecules.

• Cellular respiration involves releasing chemical energy through the breakdown of glucose and creating an energy-storing molecule called ATP

• ATP is used by all cells to do biological work

• Cellular respiration involves multiple metabolic pathways:

  • Glycolysis— occurs in the cytoplasm

  • Pyruvate oxidation— occurs in mitochondria

  • Krebs (Citric Acid Cycle)— occurs in mitochondria

  • Electron transport— occurs in mitochondria

The electron transport chain transfers energy from electrons in a series of coupled reactions

• Electron transport chain reactions occur in the membranes of chloroplasts and mitochondria, and in the cell membranes of prokaryotes

• An ETC facilitates a series of coupled reactions used during cellular respiration

• Electron transport chains allows for a more controlled and efficient transfer of energy

• ETC uses electron energy to establish electrochemical/proton gradients across membranes

• Electrons are delivered by electron carriers, called NADH and FADH2 to the ETC

• ATP synthase uses the proton gradient to synthesize ATP

ETC reactions occur in chloroplasts, mitochondria, and in the plasma membranes of some cells

• The highly complex organization of living cells and living systems relies on a constant input of energy

• ETC reactions are conserved processes

• In eukaryotic cells, ETCs are located in the inner mitochondrial membrane and the internal membrane of the chloroplast

• In prokaryotic cells, EETCs are located in the plasma membrane

What does the ETC do?

• Membrane proteins make up the ETC

• ETC proteins facilitate a series of coupled reactions using the energy from electrons

• High-energy electrons are donated by electron carriers, NADH and DADH

• Active transport of protons establishes a proton gradient across the membrane

• Proton gradients are maintained as a result of biological membrane impermeability to charged molecules/ ions

The flow of protons by chemiosmosis through ATP synthase drives ATP synthesis

• The process of making ATP using the stored energy of a proton gradient is referred to as oxidative phosphorylation

  • NADH and FADH2 lose high energy electrons to the ETC = oxidation

  • ATP synthase adds an inorganic phosphate to ADP, resulting in an ATP molecule = phosphorylation.

• Protons moving along the gradient (diffusion), through ATP synthase, power ATP synthesis